1. Field of the Invention
This invention relates to the field of aqueous film coating of pharmaceutical, food, confectionery, and agricultural products, and is specifically concerned with providing film coatings having an elegant, extremely glossy, and smooth appearance.
2. Description of the Prior Art
Coating of pharmaceutical dosage forms is well known in the industry. Film coating systems that impart a finished tablet gloss also are known. Cellulosic polymers, maltodextrin, and other polymers have all been used in coatings for substrates such as pharmaceutical tablets, and to some degree impart a desired "coated tablet" appearance or gloss to the pharmaceutical tablets. For example, such coatings made from coating compositions manufactured by Colorcon, of West Point, Pa., and disclosed in Colorcon U.S. Pat. Nos. 4,543,370, 4,683,256, 4,643,894, 4,725,441, 4,828,841, and 5,470,581, Colorcon U.S. patent application Ser. No. 08/778,944, and Colorcon U.S. patent application Ser. No. 08/466,939, all of said patents and said patent applications being incorporated herein by reference, have proven especially effective when used on pharmaceutical tablets.
However, such coatings, especially clear coatings void of pigments, sometimes suffer from "frost" (a white frost-like haze imparted on the tablet surface) when coated at high weight gains for a gloss coat, such as greater than 1.0% weight gain, onto pharmaceutical tablets and the like.
In Berta U.S. Pat. No. 4,820,524, a method of coating a caplet by dipping individual ends of a caplet into a gelatinous solution is disclosed, in which gelatin of bloom strength in the range of 150-270 is used, to produce a shiny film having a thickness from 5-40 mils. Berta U.S. Pat. No. 4,820,524 also discloses a failed attempt to replicate the shine obtained by dipping by spray-coating the caplets in a coating pan with a gelatin system.
Sadek et al. U.S. Pat. No. 5,146,730 discloses a method of coating a tablet by enrobing the tablet in a gelatin coating by application of respective layers of elastic gelatin film to opposite sides of the tablet. Sadek et al. U.S. Pat. No. 5,146,730 discloses that it is essential to use gelatin with bloom values in the range of 120 to 250 to produce the desired film elasticity and adhesion characteristics.
Shen U.S. Pat. No. 5,683,717 discloses a method of spray-coating substrates with a gelatin solution consisting essentially of blooming gelatin (275 bloom), a plasticizer (which is triacetin), a surface-active agent, water, and optionally a coloring agent. The solution is heated and maintained at elevated temperatures during coating, and non-typical conditions are employed in spray-coating (an inlet temperature of 40.degree. C. or less and an outlet temperature of 20.degree. C. or less) to produce the desired effect.
Becker U.S. Pat. No. 5,114,720 discloses a method for coating previously coated tablets with a solution consisting essentially of only a low bloom gelatin (from pork, calfskin or bone) and water for the purpose of imparting a low coefficient of friction, and thus an increased slipperiness and swallowability to the tablet. There is no mention of improved gloss or smoothness.
Johnson et al. U.S. Pat. No. 4,931,286 discloses a high gloss pharmaceutical tablet with an outermost coating of sodium carboxymethylcellulose and a polyethylene glycol plasticizer wherein the outermost coating is applied from a water solution by spray- coating. However, such a coated tablet has a hazy appearance.